Fit Query

Introduction

You can view the features and usage instructions of this tool in the Tool Introduction.

Fit Query

Changelog

2026.3.31
1. Added hole basis and shaft basis preferred fit keyboards. According to GB/T 1800.1—2020, based on economic factors, fits should preferably be selected from the tolerance zone codes shown in the keyboard whenever possible.
2. Clicking a keyboard button automatically imports the corresponding tolerance code and grade.

Clearance Fit

In a hole-shaft fit, when the hole size minus the mating shaft size yields a positive value, it is called clearance. A clearance fit means the hole tolerance zone is above the shaft tolerance zone, providing clearance (including fits with zero minimum clearance).
Selection guide for shaft fundamental deviations in clearance fits:
(1) a, b: Provide exceptionally large clearances; rarely used.
(2) c: Provides very large clearances; generally suitable for slow, loose running fits. Used where operating conditions are poor (e.g., agricultural machinery), where deformation occurs under load, or where large clearance is necessary for easy assembly. Recommended fit: H11/c11. The higher-grade H8/c7 fit is suitable for tight running fits where shafts operate at high temperatures, such as exhaust valves and guides in internal combustion engines.
(3) d: Generally used for IT7-IT11 grades; suitable for loose running fits such as seal caps, pulleys, idler pulleys on shafts, and large-diameter sliding bearing fits in turbines, ball mills, roll-forming and heavy bending machines, and other heavy machinery.
(4) e: Mostly used for IT7, 8, 9 grades; typically used for bearing fits requiring noticeable clearance and easy rotation, such as wide-span bearings and multi-support bearings. Higher-grade e shafts are suitable for large, high-speed, heavily-loaded supports, such as turbine engines, large electric motors, main bearings of internal combustion engines, and camshaft bearings.
(5) f: Mostly used for IT6, 7, 8 grade general transmission fits. When temperature effects are minimal, it is widely used for supports lubricated with ordinary oil (or grease), such as gearboxes, small electric motors, pumps, and shaft-to-sliding bearing fits.
(6) g: Very small fit clearance with high manufacturing cost. Not recommended for running fits except in very light-load precision devices. Mostly used for IT5, 6, 7 grades; best suited for non-rotating precision sliding fits, and also for locating fits such as pins. Examples: precision connecting rod bearings, pistons, slide valves, and wrist pins.
(7) h: Mostly used for IT4-IT11 grades. As a general locating fit, it is widely used for parts with no relative rotation. If there are no temperature or deformation effects, it can also be used for precision sliding fits.

Transition Fit

A transition fit is one in which the hole and shaft tolerance zones overlap each other; any randomly selected pair of hole and shaft may result in either clearance or interference.
Selection guide for shaft fundamental deviations in transition fits:
(1) js: Perfectly symmetrical deviation (+IT/2 and -IT/2); a fit with smaller average clearance. Mostly used for IT4-7 grades where clearance is required to be smaller than h shaft and slight interference is acceptable for locating fits, such as couplings, gear rings on steel hubs, etc. Can be assembled with a wooden mallet.
(2) k: A fit with average clearance close to zero; suitable for IT4-7 grades. Recommended for locating fits with slight interference, such as fits used to eliminate vibration. Generally assembled with a wooden mallet.
(3) m: A fit with relatively small average interference; suitable for IT4-7 grades. Generally can be assembled with a wooden mallet, but at maximum interference, considerable press-in force is required.
(4) n: Average interference slightly larger than m; rarely produces clearance. Suitable for IT4-7 grades; assembled with a hammer or press. Usually recommended for tight component fits. The H6/n5 combination results in an interference fit.

Interference Fit

An interference fit is one in which the hole size minus the mating shaft size yields a negative value.
Selection guide for shaft fundamental deviations in interference fits:
(1) p: Produces an interference fit with H6 or H7, and a transition fit with H8. For non-ferrous parts, it provides a light press fit that is easy to disassemble when needed. For steel, cast iron, or copper-steel component assemblies, it is a standard press fit.
(2) r: A medium drive fit for ferrous parts and a light drive fit for non-ferrous parts; can be disassembled when needed. With H8 hole, it produces an interference fit for diameters above 100mm and a transition fit for smaller diameters.
(3) s: Used for permanent and semi-permanent assembly of steel and iron parts; can produce considerable bonding force. When used with elastic materials such as light alloys, the fit characteristics are comparable to p shafts for ferrous parts, e.g., ring pressed onto shafts, valve seats, etc. For larger sizes, assembly by thermal expansion or shrinkage is required to avoid damaging the mating surfaces.
(4) t: A fit with larger interference. For steel and cast iron parts, it is suitable for permanent joints; can transmit torque without keys. Assembly by thermal expansion or shrinkage is required, e.g., coupling-to-shaft fits.
(5) u: This fit has large interference. Generally, verification is needed to ensure the workpiece material is not damaged at maximum interference. Assembly by thermal expansion or shrinkage is required, e.g., train wheel-to-axle fits.
(6) v, x, y, z: Fits formed by these fundamental deviations have even greater interference. They should only be applied after testing and are generally not recommended.

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